Iran’s biggest group of clerics has declared President Mahmoud Ahmadinejad’s re-election to be illegitimate and condemned the subsequent crackdown.

The statement by the Association of Researchers and Teachers of Qom is an act of defiance against the Supreme Leader, Ayatollah Ali Khamenei, who has made clear he will tolerate no further challenges to Mr Ahmadinejad’s “victory” over Mir Hossein Mousavi.

“It’s a clerical mutiny,” said one Iranian analyst. “This is the first time ever you have all these big clerics openly challenging the leader’s decision.” Another, in Tehran, said: “We are seeing the birth of a new political front.”

Professor Ali Ansari, head of Iranian Studies at St Andrews University, said: “It’s highly significant. It shows this is nowhere near resolved.”

The association’s statement also shows how deeply the political establishment is divided, and the extent to which the Supreme Leader now derives his power from military might, not moral authority. It makes it much harder for the regime to arrest Mr Mousavi and other opposition leaders.

At the weekend a top aide to Mr Khamenei demanded that Mr Mousavi and other opponents be tried for “terrible crimes”, and the elite Revolutionary Guards accused them of “trying to overthrow the Islamic establishment”.

In other developments, David Miliband, the Foreign Secretary, said yesterday that he expected the eighth of the nine British Embassy employees arrested ten days ago to be released soon but a lawyer representing the ninth — a political analyst named Hossein Rossam — said he would be charged with threatening national security.

Mr Miliband expressed “cold anger” at the way the nine had been treated.

The regime freed Iason Athanasiadis, an Anglo-Greek journalist arrested on June 19. However, a lawyer for Maziar Bahari, a Canadian-Iranian journalist working for Newsweek, said he faced charges of “instigating riots and acting against national security”. The Association of Researchers and Teachers is based in Qom, the clerical nerve centre of Iran, and includes many leading ayatollahs with impeccable revolutionary credentials and big personal followings.

The association did not support a candidate in the election, but has now lined up firmly behind Mr Mousavi. In a rebuke to the regime it declared on its website: “Candidates’ complaints and strong evidence of vote-rigging were ignored . . . Peaceful protests by Iranians were violently oppressed . . . Dozens of Iranians were killed and hundreds were illegally arrested . . . The outcome is invalid.”

It called on other clerics to speak out, demanded the release of all those arrested in the past three weeks, and directly challenged the authority of the Guardian Council, a body of 12 senior clerics that has openly backed Mr Ahmadinejad and his patron, Mr Khamenei. “How can one accept the legitimacy of the election just because the Guardian Council says so?,” it asked.

On Wednesday, a day after the Guardian Council said that the election result was final, Mr Mousavi talked of forming a new political grouping to fight an illegitimate government.

With the popular former president Mohammad Khatami and Medhi Karoubi, another defeated candidate, challenging the Government’s legitimacy, and Ali Akbar Hashemi Rafsanjani, another former president, pointedly meeting the families of those killed in street demonstrations, that coalition is beginning to take shape.

“The fact that anyone dares to condemn the election when people were calling for Mousavi and Karoubi’s heads is remarkable,” said the analyst in Tehran. “It shows there is depth to Mousavi’s support. They have not been bullied into silence, there are factions forming and this is not over.”

Mr Mousavi issued a 25-page paper detailing election abuses ranging from the printing of 14 million extra ballot papers to bribes to ballot boxes containing not a single vote for him even in his hometown.

Mr Miliband expressed fury at Mr Rossam’s detention. The charge that he had helped incite the protests had “absolutely no basis”. Mr Rossam, 44, was “an honourable, patriotic Iranian, who has been working in a completely open and transparent way for the UK”.

The European Union’s member states have protested to Iran and will consider tougher measures if Mr Rossam is not released this week. British officials are also hoping for a strong statement from Wednesday’s G8 summit.

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